Deployment algorithms for supplemental restraints such as airbags have traditionally relied almost exclusively on measured vehicle parameters such as acceleration and speed. In a typical approach, the onset of a crash event is detected when the longitudinal acceleration of the vehicle exceeds an initial threshold; in the course of the ensuing crash event, the vehicle's change in velocity is calculated by integrating the longitudinal acceleration and the airbags are deployed for occupant protection if and when the calculated change in velocity exceeds a time-varying velocity boundary curve (VBC).
The timeliness of crash discrimination and deployment can be improved through the addition of one or more remote acceleration sensors near the front of the vehicle, but this considerably increases system cost. Alternatively, it has been proposed to employ an anticipatory sensor such as a closing velocity (CV) sensor to detect the presence of an approaching object prior to collision. However, manufacturers have been reluctant to take any action based on the output of an anticipatory sensor because it is difficult or impossible to discriminate between objects that might result in a serious collision and objects that pose little or no danger to the vehicle occupants. Nevertheless, it has been suggested to use measurements such as closing velocity to determine the seriousness of an impending impact and to arm or activate a deployment algorithm. See, for example, Continental Automotive Systems' 2001 press release entitled “TEMIC: The intelligent car for maximum safety”, which is available in the press release archive of Continental Automotive Systems' website (www.conti-online.com).